steamFrame.dashboard.passthroughToggle: the SteamVR dashboard's room view
button cycles Off -> colour (Arcturus Vision camera) -> monochrome IR -> Off,
with a purple eye in colour mode. A Steam UI patch on the dock bar windows,
a CDP relay and a small Rust helper that switches the camera source through
SteamVR's IVRCameraPassthroughInternal_001 (vrclient.so from the SteamVR
install, nothing vendored). Cleanup artifact for SteamVR's client log.
Adapted from toorux/steam-frame-passthrough-toggle and
KominoVR/frame-passthrough-shortcuts (MIT), see README Credits.
